1. Field of the Invention
The present invention relates to a toner, and more particularly to a toner having improved low-temperature fixability, high temperature preservability and offset resistance. The invention further relates to a process cartridge that includes a photoreceptor, and at least one of a charger, a cleaner and an image developer, that may use the toner, and an image forming apparatus including the process cartridge.
2. Discussion of the Background
Recently, in order to save energy for fixing a toner in image forming methods such as for example photocopying, the fixing energy is required to be small. Therefore, it is necessary to control the thermal properties of the toner itself, i.e., a resin. However, a resin having a low glass transition temperature (Tg) gives a toner wherein high temperature preservability and fixability have been deteriorated, and a low-molecular-weight resin having a low F1/2 temperature has problems of occurrence of hot offset and too high glossiness. Thus, a toner having good low-temperature fixability, high temperature preservability and offset resistance has not yet been obtained by controlling the thermal properties of the resin itself.
In order to obtain the desirable low-temperature fixability, Japanese Laid-Open Patent Publications Nos. 60-90344, 64-15755, 2-82267, 3-229264, 3-41470 and 11-305486 disclose the use of a polyester resin having good low-temperature fixability and comparatively good high temperature preservability in comparison to the styrene-acrylic resins conventionally and frequently used. Japanese Laid-Open Patent Publication No. 62-63940 discloses the inclusion of a specific non-olefin crystalline polymer having a sharp melting capability at its glass transition temperature in a binder for the purpose of improving low-temperature fixability of the resultant toner. However, it cannot be said that its molecular geometry and weight are optimized.
Japanese Patent No. 2931899 and Japanese Laid-Open Patent Publication No. 2001-222138 disclose the use of a crystalline polyester having a same sharp melting capability. However, the crystalline polyester in Japanese Patent No. 2931899 has a low acid value (not greater than 5) and a low hydroxyl value (not greater than 20), and has a low affinity with a paper. Therefore, the resultant toner does not have sufficient low-temperature fixability. In addition, its molecular geometry and weight are optimized. Further, the resultant toner does not have good transferability, durability, charge stability against humidity and pulverizability or sufficient low-temperature fixability and offset resistance even in a fixing method carried out without coating a release oil or with a very slight application thereof on a fixing roller while having adequate glossiness. In Japanese Laid-Open Patent Publication No. 2001-222138, the resultant toner does not have good transferability, durability, charge stability against humidity and pulverizability or sufficient low-temperature fixability and offset resistance even in a fixing method carried out without coating a release oil or with a very slight application thereof on a fixing roller while having adequate glossiness.
Because of these reasons, a need exists for a toner having improved dispersibility and pulverizability as well as improved low-temperature fixability, high temperature preservability and offset resistance.